Conventionally, various encoding methods for compression-coding digital audio signal have been put into practical use. To be specific, when converting an analog audio signal to a digital audio signal, typically a predetermined number of bits of data are sampled every constant sampling period, so that a digital audio signal is generated. Further, a predetermined number of bits of data are compression-coded every constant sampling period by various compression methods suitable for the audio signal.
For example, there is an art in which a digital audio signal obtained by sampling an analog audio signal within an audible frequency band from 20 Hz to 20 kHz is divided into a predetermined number of bands, and various kinds of arithmetic processing for reducing amount of data, such as discrete cosine transform, are performed on each of the divided bands to encode the signal. Such process has been put into practical use as a compressed audio format such as MP3 (MPEG Audio Layer-3).
Patent document 1 discloses an example of this kind of audio signal encoding process.
[Patent document 1] International Publication (laid-open) No. 2005/004113 pamphlet